Objective: The purpose of this study was to investigate the effects of cortical bone thickness on the biomechanical performance of minscrew (mini-implant) anchorage with finite element analysis. Method: Three-dimensional finite element models were created, with various cortical thicknesses, in this study. In general, these models consisted of the cortical shell, cancellous core and miniscrew. The properties of each material were assumed to be isotropic and linear. The elastic modulus of the miniscrew, cortical bone and cancellous bone were assigned as 110 GPa, 13.7 Gpa and 1.37 GPa respectively. The Poisson ratio was 0.35 for the miniscrew, and 0.30 for the two bony materials. The thickness of cortical shell was ranged from 0mm to 2.5mm, with a 0.5mm interval. A 0.025N force was applied at the center of screw head toward mesial direction with various angles of 0¢X, 45¢X and 90¢X. The nodes on the bottom layer of the bone structure were fixed in all directions to represent the boundary condition. Results: The results showed that the distributions of von Mises stress were intense at the screw-bone interface. The major stress concentration was exhibited at the regions of cortical bone, while the peak stress was around the first thread of the miniscrew. The thickness of cortical shell would affect the stress distributions but the loading direction was also an important factor. Conclusions: The failure of the miniscrew anchorage, such as loosing, should relate significantly with its mechanical conditions. The cortical shell plays a vital role in providing the foundation for miniscrew stability and the thickness of this shell as well as the loading direction are crucial for the biomechanical evaluation of the minscrew.

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